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Species · California · BBS 2026 Release · 1966–2025

Marbled Murrelet Population Trend in California

All statesSeabirds

Marbled Murrelet in California has edged down: down 18% on the route-weighted index since 1985.

-18%Since 1985TrendPercent change in the route-weighted abundance index between a smoothed baseline window and the most recent one. It tracks direction, not absolute population.Full methodology →
6Routes In StateSurvey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
34YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Marbled Murrelet Trends in CaliforniaNotable signalsLong-arc shifts the engine flags automatically — sustained declines or increases large enough to stand out from year-to-year noise.Full methodology →

No notable trend signals for Marbled Murrelet in California. See the full index history below.

Marbled Murrelet Population Forecast in California

If the recent trend holds, Marbled Murrelet in California is projected to stay roughly flat through 2030, near 0.02 (95% range 0.00–0.23). A 5-year backtest shows a typical error of ±115%, with 100% of held-out values landing inside the 95% band.

n/aChange by 2030TrendPercent change in the route-weighted abundance index between a smoothed baseline window and the most recent one. It tracks direction, not absolute population.Full methodology →
0.02Projected 2030 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
0.00–0.2395% range95% rangeThe 95% uncertainty band around the projection at the forecast horizon. The true value should land inside it most of the time.Full methodology →
±115%Backtest errorBacktest errorTypical error when we hold out the most recent years, forecast them, and compare to what actually happened. Lower means a more trustworthy projection.Full methodology →
If the recent trend holds, Marbled Murrelet in California is projected to stay roughly flat through 2030, near 0.02 (95% range 0.00–0.23). A 5-year backtest shows a typical error of ±115%, with 100% of held-out values landing inside the 95% band.19802030
Projection of the recent trend (dashed) with 80/95% bands — a projection, not a prediction. Habitat, climate, and land use are not modeled.
YearProjected indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →95% low95% rangeThe 95% uncertainty band around the projection at the forecast horizon. The true value should land inside it most of the time.Full methodology →95% high95% rangeThe 95% uncertainty band around the projection at the forecast horizon. The true value should land inside it most of the time.Full methodology →
20260.030.000.24
20270.030.000.24
20280.030.000.24
20290.030.000.23
20300.020.000.23

Marbled Murrelet Survey Routes in California

Routes recording Marbled Murrelet in California.
Recent countThe raw number of individuals recorded on this route in its most recent survey year. A single-route tally, not a trend.Full methodology →
Redwood N.P. 21920132012
Holmes320251992
Pescadero320191992
Honeydew219821982
Redwood N.P.120052004
Fish Rock120001980

Marbled Murrelet Population Trend in Other States

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Source: USGS North American Breeding Bird Survey, retrieved 2026-08-14.